This invention relates to a flexible process and machine for drilling oil-holes in different positions in a range of various types of crankshaft, in medium- or high-capacity production, for combustion engines (cars, . . . ).
Oil-holes may be situated in various positions lengthways and widthways on the longitudinal axis of a crankshaft, as well as in different positions around the circumference described when turning on this longitudinal axis. They may also be perpendicular or with various angles of inclination with respect to this longitudinal axis of the crankshaft.
Until the automotive industry concerned itself with the concept of flexibility, the machining described was undertaken by transfer units (multi-station lines), with each station drilling one of various holes. This solution has been valid in times of few changes in the dimension and shape of crankshafts, when an automobile engine was certain to have an extended life on the market. But now that changes are frequent, both machine and process need to be flexible to adapt to crankshafts with dimensional and geometrical modifications, as well as variations in the position/inclination of the oil-holes and also in the number of such holes. This adaptation needs to be rapid, simple and low-cost, due to the frequency of such a need.
There is another factor that has been changing in recent years: when a new automobile engine is launched onto the market, there are always doubts about the demand and any initial forecast may be miscalculated, either above or below the mark. For this reason, automobile manufacturers nowadays prefer production methods that begin with low-scale investment and production and later, if there is a growing response from the market, to gradually add new productive units the same as at the beginning. If the first unit is enough for a production volume of up to 50,000 pieces/year, they will need to add a second unit when there is a demand for up to 100,000/year, a third unit if there is a further demand and so on.
These factors cannot be tackled with multi-station transfer units, because they are not very flexible, nor do they admit progressive investment in line with escalating production brought on by increasing demand, since these are high-cost and high-production machines from the outset.
Furthermore, the diversity of oil-hole placement, explained previously, is not possible in traditional machining centres, with their X, Y and Z axes, at least in mid-high production level. Also, there is the problem of the additional W axis which is needed to position independently the drill guide bushings, since this fourth axis does not exist in traditional machining centres. Neither is there a special device to enable occasional automatic changing of the tool+guide bushing, and at other times just the bushing, because the tool is being used for the next drilling, but the bushing needs to be changed because it requires a different plane on the front end, to adapt it to the plane of the zone of the crankshaft it is resting on.
Because of all this, there is a need for a machine for drilling oil-holes in different positions and in a varied range of crankshafts, it needs to be flexible and at the same time a productive unit capable of being included in a production line in a quantity that increases as production increases.
There has been a previous attempt to meet this ambitious objective, but it has not produced the expected results, as it has important drawbacks which in medium-high production are a great inconvenience for an industry as demanding as the automotive industry. Below are some of the known drawbacks of this previous attempt, which for simplicity's sake will be referred to as "I A" (U.S. Pat. No. 5,759,140):
a) The machine has to be capable of working with gun drills which have a collector for the chips produced during the drilling, as well as with twist drills with no collector, and then the chips are scattered over the working area. The second alternative requires the layout of the working area to be such that there is no piling up of the chips on the crankshaft-bearing tools and on adjoining mechanisms, making it essential for the chips to be eliminated by falling through cleared areas and without any obstacle.
In the "I A" machine, the crankshafts are supported on a box-shaped rectangular frame, almost closed in on one side and with an opening on the other side for loading and unloading the crankshafts. This box-frame pivots on a horizontal axis supported on two opposing bearings. The pivoting is so that the longitudinal axes of the crankshafts situated in the box-frame can take various positions:
1.sup.st position: horizontal during the loading/unloading of the crankshafts.
2.sup.nd position: vertical, when drilling the holes perpendicular to the longitudinal axis of the crankshafts.
3.sup.rd position: inclined upwards when drilling the holes which are inclined in one direction with respect to the longitudinal axis of the crankshafts.
4.sup.th position: inclined downwards when drilling holes with the opposite inclination to the previous one.
The box-frame is almost closed in on one side and also receives the crankshafts, as well as the positioning and fixture mechanisms, together with the turning mechanisms of the crankshafts on their longitudinal axis and other necessary mechanisms, piping etc. All these elements are piled up in the box-frame. And in the 3.sup.rd and 4.sup.th positions, which are inclined, the chips from drills with twist drills fall directly and in great quantity onto the box-frame and all the mechanisms contained therein, and as they have no free-fall, they start blocking up crevices and anywhere else they can find to settle. This is a serious drawback, and in subsequent loading/unloading of crankshafts, the piling up of chips will cause malfunctions which are inadmissible in mid-high production.
In the summary of the invention which is presented further on, point a.sub.1) describes its layout which is totally different to that of "I A", the way in which the drawbacks of "A I" are avoided and the lack of comparison in layout and results between "I A" and this invention, both in this aspect and in those which are set out afterwards.
b). The problem of chips scattering all over the work area, when drilling with twist drills, is avoided when working with gun drills, because they have a chips collector in the shape of a collecting bin joined to the outlet pipe. But with "I A" there now arises another problem and serious at that. The collecting bin and the outlet pipe together are fairly bulky, and if the chips are of steel, they need to be very bulky, since steel chips are sizeable and difficult to evacuate. And the external configuration of this apparatus collides with the crankshaft-bearing box-frame and with its piled up mechanisms. This occurs in the 3.sup.rd and 4.sup.th positions, both inclined, as described in a). And to avoid this collision, one has to make do with combined collecting bin/outlet pipe apparatuses that are insufficient for their function, giving rise to obstructions in the evacuation of chips, continual stoppages and maintenance requirements that are unacceptable in mid-high production.
See b.sub.1) for the totally different layout of this invention that avoids this problem inherent in "I A".
c). The pivoting on two bearings of the box-frame which supports the crankshafts in "I A" leaves this device supported only on its centrally-situated pivotal axis and the rest is hanging free. This is too much to be hanging free. Crankshafts are lengthy pieces, and at each end are the referencing and support elements, which make the sub-unit even longer and they can give some 500-600 mm to the right and to the left of the pivoting, with no additional support but for the pivotal axis. The other side of the rectangle of the box-frame is also rather large and the crankshafts, together with all the mechanisms in the box-frame make up a great weight, forming an enormous and heavy mobile sub-unit, which also bears the drilling forces. This situation is not helped by just the pivotal axis, even by adding braking to the pivotal axis, as the zones hanging free are some distance away. In this respect, the inclinations of the crankshafts for holes to be drilled at particular angles to the longitudinal axis of the crankshaft are not precise, as they are affected by the imprecision caused by the zones hanging free, lacking any support. In addition, the zones hanging free, acting as a counterweight, do not favour precision in inclined positioning power-controlled by the pivoting activator.
See c.sub.1) for how this invention, with a totally different layout to that of "I A" avoids these drawbacks.
d). When turning of the crankshafts on their respective longitudinal axes so that the circumferential position for beginning the drilling of the next hole is aligned with the corresponding tool, is effected by "I A" with transmission by a toothed belt connected to three toothed pulleys, one of which is on the servomotor and the other two on the shafts turning the two crankshafts. The transmission has a circuit in the shape of an isosceles triangle, with pulleys at the three vertices. This layout has the following drawbacks:
The toothed belt, as a result of long-term use, becomes longer and this produces gaps in the gearing with the toothed pulleys, giving rise to defects in the precise circumferential positioning of the crankshafts when turning on their longitudinal axes.
The toothed belts have a limited life and tend to break, requiring their periodical replacement. This gives rise to maintenance problems, because the transmission is situated in an area with difficult access, as it is surrounded by a large number of mechanisms that get in the way.
The transmission, with its belt, its three toothed pulleys, protective covering and servomotor form a bulky sub-unit which aggravates the problems of space produced by the box-frame which houses the crankshafts and the rest of the mechanisms. This makes maintenance access to these mechanisms difficult. It also creates an obstruction in the box-frame sub-unit, affecting the elimination of chips (see point a).
There is a further problem. With the drawbacks already mentioned, the layout is applicable to two crankshafts per cycle. But there are further problems if there are, for example, three crankshafts, due to the difficulty of belt transmission between one activating axis (the servomotor) and three activated axes in a line.
See d.sub.1) for how this invention has none of these drawbacks, due to a totally different layout.
e). The W axis of the machining module bears the guide bushings of the tools. When using gun drills, the bushings rest with spring pressure on the area of the crankshaft where drilling is begun, so that the chips and pressure coolant can be evacuated. With twist drills, the bushings are placed a little apart from this area, so that the chips and coolant can escape through this small space. The W axis runs parallel to the Z axis (the tool feed) of the machining module, and is activated independently, so that first the W axis moves into place until the bushings are situated in their correct positions, then the Z axis moves into place to begin drilling, while W remains static. In the "I A" machine, the W axis is in the shape of a quill unit, emerging from the body carrying the drill bushings and positioning itself in between the two bushings. This layout has the following drawbacks:
Positioning quill unit between the two bushings is only possible when two crankshafts per cycle are being drilled. But if only one or more than two crankshafts are being drilled, as the machining module has to carry one or more than two bushings, the position of the quill with respect to the bushings is not balanced, resulting in problems related to parts hanging free, imbalances and various other complications affecting the stability of the guide bushings during drilling and consequently the precise positioning of the holes.
As the quill unit is mounted in the body carrying the guide bushings, when Z moves while drilling, this simultaneously moves W forward. But since, as was previously mentioned, W with its guide bushings has to remain static during the drilling process, this means that the independent activation of W has to move back while Z moves forward. Thus, the relative position between the crankshafts and their respective guide bushings is unchanged. But this combination of Z moving forward while W moves back requires an interpolation between the two servoactivators to be programmed, an interpolation that complicates programming. As this is supposed to be a flexible machine and therefore suitable for drilling different kinds of crankshaft, any complication as described above is counter-productive in terms of maximum operative simplicity.
The quill unit-shaped W axis gives rise to some overhang between the support carrying the guide bushings and the seat of the quill unit on the body carrying the bushings. With the option of drilling with gun drills, the collecting bin with the outlet pipe, designed to collect the chips, is also connected to the support carrying the guide bushings. This makes up a bulky and weighty sub-unit with a lot of overhang with respect to the seating of the quill unit, and it does not have the strength and stability needed to support such a sub-unit. This poses snags and drawbacks of application, even when two crankshafts per cycle are being drilled and the quill unit is between the two bushings. But these drawbacks are intensified when drilling just one or more than two crankshafts per cycle: the position of the quill unit with respect to the bushings adds further problems (see the first drawback in e).
With all these problems, it is evident that the quill unit is not a good solution for the W axis. See e.sub.1) for how this invention eliminates all these problems with an independent module instead of a quill unit mounted in the bushings unit.
f). In mid-high production, the loading and unloading of pieces into the machine is of relevant importance, and more so with pieces of certain weight and volume, as is the case with crankshafts, particularly if several pieces per cycle are being machined. Usually automatic loading/unloading is used, either with handling gantries or similar systems. For this reason, the loading/unloading station needs to be endowed with suitable characteristics, and even extra options in order to meet special circumstances which arise in mid-high production. The aim is to be able to favourably organise such an important aspect, whatever the circumstances attached to each particular application. The flexibility of a machine exists for a reason--to be able to adapt to a whole range of situations. The "I A" machine does not offer these suitable characteristics or additional options. The loading/unloading station is inflexible and precarious. It is inflexible for automatic as well as manual loading/unloading. This involves hazards for the operator in manual loading/unloading if the automatic function has had to be stopped temporarily because of a breakdown or for maintenance. As these machines are situated in a line with various productive units, attended by a lengthy crankshaft transport and handling system, working simultaneously with a number of arms on their respective production units, if there is a malfunction at one of these stations (for example the grip clamps for handling the crankshafts), then the automatic load/unload function has to be disabled, yet the overall transport and handling system is still functioning at all the stations, and the operator manually loading and unloading at the affected station faces problems and even hazards due to the difficulty of establishing complete safety conditions because the overall system is still operating above.
See f.sub.1) for how this invention offers ideal characteristics and extra options for loading/unloading, based on a totally different layout.
g). For the automatic changing of tools+their guide bushings, or just the bushings when applicable, the "I A" machine requires an additional "U" axis which involves columns, a gantry, a module for the elements to be changed, together with their endless belt-driven mechanisms, as well as other complementary mechanisms. All this involves considerable bulk and which needs to fit and move in the hazardous gap between the machining module and the crankshaft-carrying sub-unit. So much so that this sub-unit means placing the box-frame with all it contains (crankshafts, fixtures, etc.) vertically, otherwise there would not be room to move the U axis that automatically changes the tool etc. This is a solution that is complicated, a costly investment, awkward and not at all ideal for a flexible machine.
See g.sub.1) for a completely new solution with this invention, which avoids the drawbacks of "I A".
h) For the purposes of productivity with a machine devoted to mid-high production, if the aim is to achieve the required flexibility, further options are desirable, such as:
The machine needs two stations, one for machining and the other for loading/unloading the pieces. Thus one can load/unload at one station, while machining at the other, thereby saving all the time spent handling, loading/unloading and supporting the pieces, and so increasing productivity, with only a slightly higher investment, because of the duplication of fixtures.
Similarly, one could establish cells, with two machining modules facing each other and a centrally-situated sub-unit carrying the crankshafts and their tools, also double-sided. This would be like a "mirror" cell. It would duplicate production, but the investment would be less than double.
These options are impossible with "I A", while thanks to its totally different overall layout, this invention, as can be seen in h.sub.1) and in the description and plans, does make them possible.
i). A serious problem in mid-high production is the lack of direct and easy access to all parts of the machine whenever adjustment, checking or maintenance is required. This demands the intelligent laying out of all the mechanisms/sub-units/units. This is not the case with "I A", which is an agglomeration of parts which get in the way of each other.
On the other hand, see i.sub.1) and the plans for how this invention is uncluttered and accessible from all sides thanks to its layout, which has eliminated every unnecessary complication and agglomeration.